R Nitu Meteorological Service of Canada AMS, Phoenix, AZ 12 Jan 2009

1. WMO CIMO SurveyNational Summaries of Methods and Instruments for Solid Precipitation Measurement- Preliminary results - R Nitu Meteorological Service of Canada AMS, Phoenix, AZ 12 Jan 2009

2. Scope • The WMO CIMO-XIV, has tasked the Expert Team on Surface-Based Instrument Intercomparisons and Calibration Methods to: • assess the methods of measurement and observation of solid precipitation at automatic stations: • assessing the need for an intercomparison of methods and equipment for automatic snowfall, snow depth, precipitation measurements, and develop an intercomparison plan.

3. 1986-1993 WMO Solid Precipitation Measurement Intercomparison • assessed national methods of measuring solid precipitation against methods of known accuracy and reliability (primarily manual); • determined wind related errors in national methods of measuring solid precipitation; • derived standard methods for adjusting solid precipitation measurements; • introduced a reference method of solid precipitation measurement for general use to calibrate any type of precipitation gauge. • Final report: WMO/TD- No. 872, 1998, WMO Solid Precipitation Measurement Intercomparison, by B.E. Goodison and P.Y.T. Louie (both Canada), and D. Yang (China)

4. 2008 CIMO Survey on Methods and Instruments for Solid Precipitation • Distributed July 2008, through CIMO Secretariat. • Goals of the survey: • The extent of using automatic instruments for measuring precipitation (liquid and solid); • Parameters measured, instruments used and their configuration; • Identify adjustments applied to precipitation measurements; • Summary of derived solid precipitation parameters from automatic stations measurements; • Summary oftesting/developing new instruments and methods of measurement of solid precipitation parameters

5. Questions: • How many stations use automatic precipitation gauges? • How many stations use shields with such gauges as recommended by WMO? If so what type of shielding? • How many stations use heated gauges? • How many stations use other type of electronic sensors to measure precipitation, e.g. distrometers, snow pillows, etc?

6. Survey Results • By Dec 2008: • 53 Member countries responded to the 2008 CIMO Questionnaire (46% of the global landmass) operate precipitation measurement programs using a combination of manual observations and automatic instruments: • 41,187 stations, • Average density: 1 station/1100 sq Km. • 34 of the respondents (28% of the land mass) measure solid precipitation: • 17,242 stations, • Average density: 1 station/2200 sq Km.

7. How many stations use automatic precipitation gauges? • Measuring the amount of precipitation (41,187 stations, 53 countries): • 82% of stations use manual means of observation; • 18% of stations use automatic instruments in 33 participating Member countries. • Measuring snow on the ground and snowfall (17,242 stations, 34 countries): • 93% of stations use manual means of observation; • 7% of stations use automatic sensors.

8. Automatic instruments in use Amount of precipitation: Weighing type gauges: measuring the mass accumulated in its bucket over a given period. Tipping bucket type gauges: integrating over time the mass falling onto one of two small buckets in a tipping balance.

9. Automatic instruments in use Weighing Type Gauges: • used in 18 NMHSs, • Six manufacturers (Geonor, OTT, Vaisala, MPS Systems, Meteoservis, and Belfort); • Collecting area: 200, 400, 500 cm2 • Collecting capacity: 250 to 1000 mm • Heating: optional (Geonor, OTT, Vaisala), standards feature (MPS Systems, Meteoservis) Tipping Bucket Type Gauges: • Used in 22 countries; • 28 different types of instruments from 21 manufacturers; • The majority have heating circuits (funnel, collecting ring); • Sensitivity: 0.1;0.2;0.25;0.5 mm of precipitation; • Collecting area: 200 to 1000 cm2.

10. How many stations use shields with gauges, as recommended by WMO? If so, what type of shielding? • Overall, the automatic gauges: • 28% used with windshields • 72% do not have windshields • Weighing type gauges (WG): • 78% of WG use single wind shields (Alter, Tretyakov, Nipher); • 22% of WG do not have wind shields; • Tipping Bucket type Gauges: • 30% configured with wind shields (Japan, USA) • 1% configured with windshields in 6 other countries; • 69% do not have windshields

11. Automatic Instruments for Solid Precipitation • 13 participating countries use automatic instruments for snow on the ground and snowfall; • 7% of sites reporting solid precipitation; • Types of instruments: • sonic ranging sensors, • optical forward scatter sensors; • snow pillow sensors. • Sensors per site: 1-3; SR-50:

12. Next steps • Final report on the Questionnaire results: mid 2009. • Evaluation of results by the Expert team on Surface Instrument Intercomparison and Calibration Methods. • In cooperation with their representatives, document the needs for precipitation measurement of WMO Technical Commissions and Programs. • Assess the need for an intercomparison of methods and equipment for automatic snowfall, snow depth, precipitation measurements.

13. Intercomparison? Potential Outcomes: • Relative performance of measurement of gauges in use. • Efficiency and configuration of shields for precipitation gauges, in particular those measuring solid precipitation (snow). • The re-evaluation of the Double Fence Intercomparison Reference (DFIR) using automatic gauges. • Development of adjustment curves using hourly precipitation and 2-meter wind during the precipitation events.

14. Thank you! Rodica Nitu Meteorological Service of Canada Rodica.nitu@eg.gc.ca